#include<bits/stdc++.h>
using namespace std;
#define int long long
signed main() {
	int n;
	cin >> n;
	int preCnt = 0, preNum = 1, nowCnt;
	int ans = 1;
	for (int i = 1; i <= n; i++) {
		preNum *= i;
		nowCnt = 0;
		while (preNum % 10 == 0) {
			nowCnt++;
			preNum /= 10;
		}
		preCnt += nowCnt;
		if (preCnt % 2 == 0)
			ans++;
	}
	cout << ans;
	return 0;
}
